The order Hymenochaetales of white rot fungi contain some of the most aggressive wood decayers causing tree deaths around the world. Despite their ecological importance and the impact of diseases they cause, little is known about the evolution and transmission patterns of these pathogens. Here, we sequenced and undertook comparative genomic analyses of Hymenochaetales genomes using brown root rot fungus Phellinus noxius, wood-decomposing fungus Phellinus lamaensis, laminated root rot fungus Phellinus sulphurascens and trunk pathogen Porodaedalea pini. Many gene families of lignin-degrading enzymes were identified from these fungi, reflecting their ability as white rot fungi. Comparing against distant fungi highlighted the expansion of 1,3-beta-glucan synthases in P. noxius, which may account for its fast-growing attribute. We identified 13 linkage groups conserved within Agaricomycetes, suggesting the evolution of stable karyotypes. We determined that P. noxius has a bipolar heterothallic mating system, with unusual highly expanded ~60 kb A locus as a result of accumulating gene transposition. We investigated the population genomics of 60 P. noxius isolates across multiple islands of the Asia Pacific region. Whole-genome sequencing showed this multinucleate species contains abundant poly-allelic single nucleotide polymorphisms with atypical allele frequencies. Different patterns of intra-isolate polymorphism reflect mono-/heterokaryotic states which are both prevalent in nature. We have shown two genetically separated lineages with one spanning across many islands despite the geographical barriers. Both populations possess extraordinary genetic diversity and show contrasting evolutionary scenarios. These results provide a framework to further investigate the genetic basis underlying the fitness and virulence of white rot fungi.
        
Title: A comprehensive review of UDP-glucuronosyltransferase and esterases for drug development Oda S, Fukami T, Yokoi T, Nakajima M Ref: Drug Metab Pharmacokinet, 30:30, 2015 : PubMed
UDP-glucuronosyltransferase (UGT) and esterases are recognized as the most important non-P450 enzymes because of their high contribution to drug metabolism. UGTs catalyze the transfer of glucuronic acid to hydroxyl, carboxyl, or amine groups of compounds, whereas esterases hydrolyze compounds that contain ester, amide, and thioester bonds. These enzymes, in most cases, convert hydrophobic compounds to water-soluble metabolites to facilitate the elimination of compounds from the body. Information about these enzymes is steadily increasing, although our knowledge is still behind our understanding of P450. This review gives an overview of recent findings in UGT and esterases studies focusing on tissue distribution, gene regulation, substrate and inhibitor specificity, and species differences. In particular, the absolute protein content of UGT isoforms and esterases in human tissues could be available. In the field of esterases, it is becoming clear that enzymes other than carboxylesterase are involved in drug hydrolysis. In addition, there is an interesting interplay between UGTs and esterases in the formation and hydrolytic deglucuronidation of acyl-glucuronide, which is considered to be a reactive metabolite. With the growing awareness of the importance of non-P450 enzymes in drug development, issues that should be resolved are discussed.
        
Title: An Orphan Esterase ABHD10 Modulates Probenecid Acyl Glucuronidation in Human Liver Ito Y, Fukami T, Yokoi T, Nakajima M Ref: Drug Metabolism & Disposition: The Biological Fate of Chemicals, 42:2109, 2014 : PubMed
Probenecid, a widely used uricosuric agent, is mainly metabolized to probenecid acyl glucuronide (PRAG), which is considered a causal substance of severe allergic or anaphylactoid reactions. PRAG can be hydrolyzed (deglucuronidated) to probenecid. The purpose of this study was to identify enzymes responsible for probenecid acyl glucuronidation and PRAG deglucuronidation in human livers and to examine the effect of deglucuronidation in PRAG formation. In human liver homogenates (HLHs), the intrinsic clearance (CLint) of PRAG deglucuronidation was much greater (497-fold) than that of probenecid acyl glucuronidation. Evaluation of PRAG formation by recombinant UDP-glucuronosyltransferase (UGT) isoforms and an inhibition study using HLHs as an enzyme source demonstrated that multiple UGT isoforms, including UGT1A1, UGT1A9, and UGT2B7, catalyzed probenecid acyl glucuronidation. We found that recombinant alpha/beta hydrolase domain containing 10 (ABHD10) substantially catalyzed PRAG deglucuronidation activity, whereas carboxylesterases did not. Similar inhibitory patterns by chemicals between HLHs and recombinant ABHD10 supported the major contribution of ABHD10 to PRAG deglucuronidation in human liver. Interestingly, it was demonstrated that the CLint value of probenecid acyl glucuronidation in HLHs was increased by 1.7-fold in the presence of phenylmethylsulfonyl fluoride, which potently inhibited ABHD10 activity. In conclusion, we found that PRAG deglucuronidation catalyzed by ABHD10 suppressively regulates PRAG formation via multiple UGT enzymes in human liver. The balance of activities by these enzymes is important for the formation of PRAG, which may be associated with the adverse reactions observed after probenecid administration.
        
Title: N-Glycosylation during translation is essential for human arylacetamide deacetylase enzyme activity Muta K, Fukami T, Nakajima M, Yokoi T Ref: Biochemical Pharmacology, 87:352, 2014 : PubMed
Human arylacetamide deacetylase (AADAC) can hydrolyze clinical drugs such as flutamide, phenacetin, and rifamycins. AADAC is a glycoprotein, but the role of glycosylation remains unclear. In the present study, we investigated the effect of glycosylation on AADAC enzyme activity. Immunoblot analysis of mutant AADACs that contained an asparagine (N, Asn) to glutamine (Q, Gln) substitution at either residue 78 or 282 (N78Q or N282Q) showed a different migration compared with the wild-type protein. A mutant AADAC that contained N to Q substitutions at both residue 78 and 282 (N78Q/N282Q) showed a similar migration to AADAC in human liver microsomes (HLM) treated with endoglycosidase H (Endo H), which produces deglycosylated proteins. This result indicated that AADAC was glycosylated at both N78 and N282. Mutant types of AADAC with the N282Q and the N78Q/N282Q substitutions showed dramatically lower phenacetin hydrolase activity than did the wild-type protein. The treatment of wild-type AADAC-expressing HuH-7 cells with tunicamycin, which produces unglycosylated protein, decreased AADAC enzyme activity. However, the treatment of the HLM with Endo H caused no decrease of AADAC activity. Thus, the oligosaccharide chain, per se, was not important for AADAC activity in the mature form. The mutant types of AADAC containing the N282Q and the N78Q/N282Q substitutions were not detected by immunoblotting analysis after non-reducing SDS-PAGE, suggesting that the glycosylation of AADAC at N282 was important for proper protein folding. Overall, this study found that the translational, but not post-translational, N-glycosylation of AADAC plays a crucial role in regulating AADAC enzyme activity.
        
Title: Screening of specific inhibitors for human carboxylesterases or arylacetamide deacetylase Shimizu M, Fukami T, Nakajima M, Yokoi T Ref: Drug Metabolism & Disposition: The Biological Fate of Chemicals, 42:1103, 2014 : PubMed
Esterases catalyze the hydrolysis of therapeutic drugs containing esters or amides in their structures. Human carboxylesterase (CES) and arylacetamide deacetylase (AADAC) are the major enzymes that catalyze the hydrolysis of drugs in the liver. Characterization of the enzyme(s) responsible for drug metabolism is required in drug development and to realize optimal drug therapy. Because multiple enzymes may show a metabolic potency for a given compound, inhibition studies using chemical inhibitors are useful tools to determine the contribution of each enzyme in human tissue preparations. The purpose of this study was to find specific inhibitors for human CES1, CES2, and AADAC. We screened 542 chemicals for the inhibition potency toward hydrolase activities of p-nitrophenyl acetate by recombinant CES1, CES2, and AADAC. We found that digitonin and telmisartan specifically inhibited CES1 and CES2 enzyme activity, respectively. Vinblastine potently inhibited both AADAC and CES2, but no specific inhibitor of AADAC was found. The inhibitory potency and specificity of these compounds were also evaluated by monitoring the effects on hydrolase activity of probe compounds of each enzyme (CES1: lidocaine, CES2: CPT-11, AADAC: phenacetin) in human liver microsomes. Telmisartan and vinblastine strongly inhibited the hydrolysis of CPT-11 and/or phenacetin, but digitonin did not strongly inhibit the hydrolysis of lidocaine, indicating that the inhibitory potency of digitonin was different between recombinant CES1 and liver microsomes. Although we could not find a specific inhibitor of AADAC, the combined use of telmisartan and vinblastine could predict the responsibility of human AADAC to drug hydrolysis.
PURPOSE: To clarify the role of ABCB1, ABCG2, and CYP3A in blood and brain exposure of everolimus using knockout mouse models. EXPERIMENTAL DESIGN: We used wild-type, Abcb1a/1b(-/-), Abcg2(-/-), Abcb1a/1b;Abcg2(-/-), and Cyp3a(-/-) mice to study everolimus oral bioavailability and brain accumulation. RESULTS: Following everolimus administration, brain concentrations and brain-to-liver ratios were substantially increased in Abcb1a/1b(-/-)and Abcb1a/1b;Abcg2(-/-), but not Abcg2(-/-)mice. The fraction of everolimus located in the plasma compartment was highly increased in all knockout strains. In vitro, everolimus was rapidly degraded in wild-type but not knockout plasma. Carboxylesterase 1c (Ces1c), a plasma carboxylesterase gene, was highly upregulated ( approximately 80-fold) in the liver of knockout mice relative to wild-type mice, and plasma Ces1c likely protected everolimus from degradation by binding and stabilizing it. This binding was prevented by preincubation with the carboxylesterase inhibitor BNPP. In vivo knockdown experiments confirmed the involvement of Ces1c in everolimus stabilization. Everolimus also markedly inhibited the hydrolysis of irinotecan and p-nitrophenyl acetate by mouse plasma carboxylesterase and recombinant human CES2, respectively. After correcting for carboxylesterase binding, Cyp3a(-/-), but not Abcb1a/1b(-/-), Abcg2(-/-), or Abcb1a/1b;Abcg2(-/-)mice, displayed highly (>5-fold) increased oral availability of everolimus. CONCLUSIONS: Brain accumulation of everolimus was restricted by Abcb1, but not Abcg2, suggesting the use of coadministered ABCB1 inhibitors to improve brain tumor treatment. Cyp3a, but not Abcb1a/1b, restricted everolimus oral availability, underscoring drug-drug interaction risks via CYP3A. Upregulated Ces1c likely mediated the tight binding and stabilization of everolimus, causing higher plasma retention in knockout strains. This Ces upregulation might confound other pharmacologic studies. Clin Cancer Res; 20(12); 3133-45. (c)2014 AACR.
        
Title: Prilocaine- and lidocaine-induced methemoglobinemia is caused by human carboxylesterase-, CYP2E1-, and CYP3A4-mediated metabolic activation Higuchi R, Fukami T, Nakajima M, Yokoi T Ref: Drug Metabolism & Disposition: The Biological Fate of Chemicals, 41:1220, 2013 : PubMed
Prilocaine and lidocaine are classified as amide-type local anesthetics for which serious adverse effects include methemoglobinemia. Although the hydrolyzed metabolites of prilocaine (o-toluidine) and lidocaine (2,6-xylidine) have been suspected to induce methemoglobinemia, the metabolic enzymes that are involved remain uncharacterized. In the present study, we aimed to identify the human enzymes that are responsible for prilocaine- and lidocaine-induced methemoglobinemia. Our experiments revealed that prilocaine was hydrolyzed by recombinant human carboxylesterase (CES) 1A and CES2, whereas lidocaine was hydrolyzed by only human CES1A. When the parent compounds (prilocaine and lidocaine) were incubated with human liver microsomes (HLM), methemoglobin (Met-Hb) formation was lower than when the hydrolyzed metabolites were incubated with HLM. In addition, Met-Hb formation when prilocaine and o-toluidine were incubated with HLM was higher than that when lidocaine and 2,6-xylidine were incubated with HLM. Incubation with diisopropyl fluorophosphate and bis-(4-nitrophenyl) phosphate, which are general inhibitors of CES, significantly decreased Met-Hb formation when prilocaine and lidocaine were incubated with HLM. An anti-CYP3A4 antibody further decreased the residual formation of Met-Hb. Met-Hb formation after the incubation of o-toluidine and 2,6-xylidine with HLM was only markedly decreased by incubation with an anti-CYP2E1 antibody. o-Toluidine and 2,6-xylidine were further metabolized by CYP2E1 to 4- and 6-hydroxy-o-toluidine and 4-hydroxy-2,6-xylidine, respectively, and these metabolites were shown to more efficiently induce Met-Hb formation than the parent compounds. Collectively, we found that the metabolites produced by human CES-, CYP2E1-, and CYP3A4-mediated metabolism were involved in prilocaine- and lidocaine-induced methemoglobinemia.
        
Title: The emerging role of human esterases Fukami T, Yokoi T Ref: Drug Metab Pharmacokinet, 27:466, 2012 : PubMed
In this review, novel aspects of the role of esterases, which contribute to the metabolism of 10% of therapeutic drugs, are described. Esterases hydrolyze the compounds that contain ester, amide, and thioester bonds, which cause prodrug activation or detoxification. Among esterases, carboxylesterases are well known to be involved in the hydrolysis of a variety of drugs. Additionally, other esterases have recently received attention for their pharmacological and toxicological roles. Arylacetamide deacetylase (AADAC) is involved in the hydrolysis of flutamide, phenacetin, and rifamycins. AADAC is associated with adverse drug reactions because the hydrolytic metabolites of flutamide and phenacetin appear to be associated with hepatotoxicity and nephrotoxicity/hematotoxicity, respectively. Paraoxonase and butyrylcholinesterase hydrolyze pirocarpine/simvastatin and succinylcholine/bambuterol, respectively. Although the esterases that hydrolyze the acyl-glucuronides of drugs have largely been unknown, we recently found that alpha/beta hydrolase domain containing 10 (ABHD10) is responsible for the hydrolysis of mycophenolic acid acyl-glucuronide in human liver. Because acyl-glucuronides are associated with toxicity, ABHD10 might function as a detoxification enzyme. Thus, various esterases, which include enzymes that have not been known to hydrolyze drugs, are involved in drug metabolism with different substrate specificity. Further esterase studies should be conducted to promote our understanding in clinical pharmacotherapy and drug development.
        
Title: Human alpha/beta hydrolase domain containing 10 (ABHD10) is responsible enzyme for deglucuronidation of mycophenolic acid acyl-glucuronide in liver Iwamura A, Fukami T, Higuchi R, Nakajima M, Yokoi T Ref: Journal of Biological Chemistry, 287:9240, 2012 : PubMed
Mycophenolic acid (MPA), the active metabolite of the immunosuppressant mycophenolate mofetil (MMF), is primarily metabolized by glucuronidation to a phenolic glucuronide (MPAG) and an acyl glucuronide (AcMPAG). It is known that AcMPAG, which may be an immunotoxic metabolite, is deglucuronidated in human liver. However, it has been reported that recombinant beta-glucuronidase does not catalyze this reaction. AcMPAG deglucuronidation activity was detected in both human liver cytosol (HLC) and microsomes (HLM). In this study, the enzyme responsible for AcMPAG deglucuronidation was identified by purification from HLC with column chromatographic purification steps. The purified enzyme was identified as alpha/beta hydrolase domain containing 10 (ABHD10) by amino acid sequence analysis. Recombinant ABHD10 expressed in Sf9 cells efficiently deglucuronidated AcMPAG with a K(m) value of 100.7 +/- 10.2 muM, which was similar to those in HLM, HLC, and human liver homogenates (HLH). Immunoblot analysis revealed ABHD10 protein expression in both HLC and HLM. The AcMPAG deglucuronidation by recombinant ABHD10, HLC, and HLH were potently inhibited by AgNO(3), CdCl(2), CuCl(2), PMSF, bis-p-nitrophenylphosphate, and DTNB. The CL(int) value of AcMPAG formation from MPA, which was catalyzed by human UGT2B7, in HLH was increased by 1.8-fold in the presence of PMSF. Thus, human ABHD10 would affect the formation of AcMPAG, the immunotoxic metabolite.
        
Title: Species differences in tissue distribution and enzyme activities of arylacetamide deacetylase in human, rat, and mouse Kobayashi Y, Fukami T, Nakajima A, Watanabe A, Nakajima M, Yokoi T Ref: Drug Metabolism & Disposition: The Biological Fate of Chemicals, 40:671, 2012 : PubMed
Human arylacetamide deacetylase (AADAC) is a major esterase responsible for the hydrolysis of clinical drugs such as flutamide, phenacetin, and rifampicin. Thus, AADAC is considered to be a relevant enzyme in preclinical drug development, but there is little information about species differences with AADAC. This study investigated the species differences in the tissue distribution and enzyme activities of AADAC. In human, AADAC mRNA was highly expressed in liver and the gastrointestinal tract, followed by bladder. In rat and mouse, AADAC mRNA was expressed in liver at the highest level, followed by the gastrointestinal tract and kidney. The expression levels in rat tissues were approximately 7- and 10-fold lower than those in human and mouse tissues, respectively. To compare the catalytic efficiency of AADAC among three species, each recombinant AADAC was constructed, and enzyme activities were evaluated by normalizing with the expression levels of AADAC. Flutamide and phenacetin hydrolase activities were detected by the recombinant AADAC of all species. In flutamide hydrolysis, liver microsomes of all species showed similar catalytic efficiencies, despite the lower AADAC mRNA expression in rat liver. In phenacetin hydrolysis, rat liver microsomes showed approximately 4- to 6.5-fold lower activity than human and mouse liver microsomes. High rifampicin hydrolase activity was detected only by recombinant human AADAC and human liver and jejunum microsomes. Taken together, the results of this study clarified the species differences in the tissue distribution and enzyme activities of AADAC and facilitate our understanding of species differences in drug hydrolysis.
        
Title: Contributions of arylacetamide deacetylase and carboxylesterase 2 to flutamide hydrolysis in human liver Kobayashi Y, Fukami T, Shimizu M, Nakajima M, Yokoi T Ref: Drug Metabolism & Disposition: The Biological Fate of Chemicals, 40:1080, 2012 : PubMed
Flutamide, an antiandrogen drug, is widely used for the treatment of prostate cancer. The major metabolic pathways of flutamide are hydroxylation and hydrolysis. The hydrolyzed metabolite, 5-amino-2-nitrobenzotrifluoride (FLU-1), is further metabolized to N-hydroxy FLU-1, an assumed hepatotoxicant. Our previous study demonstrated that arylacetamide deacetylase (AADAC), one of the major serine esterases expressed in the human liver and gastrointestinal tract, catalyzes the flutamide hydrolysis. However, the enzyme kinetics in human tissue microsomes were not consistent with the kinetics by recombinant human AADAC. Thus, it seemed that AADAC is not the sole enzyme responsible for flutamide hydrolysis in human. In the present study, we found that recombinant carboxylesterase (CES) 2 could hydrolyze flutamide at low concentrations of flutamide. In the inhibition assay, the flutamide hydrolase activities at a flutamide concentration of 5 muM in human liver and jejunum microsomes were strongly inhibited by a selective CES2 inhibitor, 10 muM loperamide, with the residual activities of 22.9 +/- 3.5 and 18.6 +/- 0.7%, respectively. These results suggest that CES2 is also involved in the flutamide hydrolysis in human tissues. Using six individual human livers, the contributions of AADAC and CES2 to flutamide hydrolysis were estimated by using the relative activity factor. The relative contribution of CES2 was approximately 75 to 99% at the concentration of 5 muM flutamide. In contrast, the relative contribution of AADAC increased in parallel with the concentration of flutamide. Thus, CES2, rather than AADAC, largely contributed to the flutamide hydrolysis in clinical therapeutics.
        
Title: A novel polymorphic allele of human arylacetamide deacetylase leads to decreased enzyme activity Shimizu M, Fukami T, Kobayashi Y, Takamiya M, Aoki Y, Nakajima M, Yokoi T Ref: Drug Metabolism & Disposition: The Biological Fate of Chemicals, 40:1183, 2012 : PubMed
Human arylacetamide deacetylase (AADAC) is responsible for the hydrolysis of clinically used drugs such as flutamide, phenacetin, and rifamycins. Our recent studies suggested that human AADAC is a relevant enzyme pharmacologically and toxicologically. To date, the genetic polymorphisms that affect enzyme activity in AADAC have been unknown. In this study, we found single-nucleotide polymorphisms in the human AADAC gene in a liver sample that showed remarkably low flutamide hydrolase activity. Among them, g.13651G > A (V281I) and g.14008T > C (X400Q) were nonsynonymous. The latter would be predicted to cause a C-terminal one-amino acid (glutamine) extension. The AADAC*2 allele (g.13651G > A) was found in all populations investigated in this study (European American, African American, Korean, and Japanese), at allelic frequencies of 52.6 to 63.5%, whereas the AADAC*3 allele (g.13651G > A/g.14008T > C) was found in European American (1.3%) and African American (2.0%) samples. COS7 cells expressing AADAC.1 (wild-type) exhibited flutamide, phenacetin, and rifampicin hydrolase activities with intrinsic clearance (CLint) values of 1.31 +/- 0.06, 1.00 +/- 0.02, and 0.39 +/- 0.02 mul x min(-1) x unit(-1), respectively. AADAC.2, which is a protein produced from the AADAC*2 allele, showed moderately lower or similar CLint values, compared with AADAC.1, but AADAC.3 showed substantially lower CLint values (flutamide hydrolase, 0.21 +/- 0.02 mul x min(-1) x unit(-1); phenacetin hydrolase, 0.12 +/- 0.00 mul x min(-1) x unit(-1); rifampicin hydrolase, 0.03 +/- 0.01 mul x min(-1) x unit(-1), respectively). Microsomes from a liver sample genotyped as AADAC*3/AADAC*3 showed decreased enzyme activities, compared with those genotyped as AADAC*1/AADAC*1, AADAC*1/AADAC*2, and AADAC*2/AADAC*2. In conclusion, we found an AADAC allele that yielded decreased enzyme activity. This study should provide useful information on interindividual variations in AADAC enzyme activity.
Bursaphelenchus xylophilus is the nematode responsible for a devastating epidemic of pine wilt disease in Asia and Europe, and represents a recent, independent origin of plant parasitism in nematodes, ecologically and taxonomically distinct from other nematodes for which genomic data is available. As well as being an important pathogen, the B. xylophilus genome thus provides a unique opportunity to study the evolution and mechanism of plant parasitism. Here, we present a high-quality draft genome sequence from an inbred line of B. xylophilus, and use this to investigate the biological basis of its complex ecology which combines fungal feeding, plant parasitic and insect-associated stages. We focus particularly on putative parasitism genes as well as those linked to other key biological processes and demonstrate that B. xylophilus is well endowed with RNA interference effectors, peptidergic neurotransmitters (including the first description of ins genes in a parasite) stress response and developmental genes and has a contracted set of chemosensory receptors. B. xylophilus has the largest number of digestive proteases known for any nematode and displays expanded families of lysosome pathway genes, ABC transporters and cytochrome P450 pathway genes. This expansion in digestive and detoxification proteins may reflect the unusual diversity in foods it exploits and environments it encounters during its life cycle. In addition, B. xylophilus possesses a unique complement of plant cell wall modifying proteins acquired by horizontal gene transfer, underscoring the impact of this process on the evolution of plant parasitism by nematodes. Together with the lack of proteins homologous to effectors from other plant parasitic nematodes, this confirms the distinctive molecular basis of plant parasitism in the Bursaphelenchus lineage. The genome sequence of B. xylophilus adds to the diversity of genomic data for nematodes, and will be an important resource in understanding the biology of this unusual parasite.
Rifamycins such as rifampicin, rifabutin, and rifapentine are used for the treatment of tuberculosis and induce various drug-metabolizing enzymes. Rifamycins have been reported to be mainly deacetylated by esterase(s) expressed in human liver microsomes (HLM) to 25-deacetylrifamycins, but the responsible enzyme remained to be determined. In this study, we found that recombinant human arylacetamide deacetylase (AADAC) could efficiently deacetylate rifamycins, whereas human carboxylesterases, which are enzymes responsible for the hydrolysis of many prodrugs, showed no activity. The involvement of AADAC in the deacetylation of rifamycins in HLM was verified by the similarities of the K(m) and K(i) values and the inhibitory characteristics between recombinant AADAC and HLM. Rifamycins exhibited potent cytotoxicity to HepG2 cells, but their 25-deacetylated metabolites did not. Luciferase assay using a reporter plasmid containing CYP3A4 direct repeat 3 and everted repeat 6 motifs revealed that 25-deacetylrifamycins have lesser potency to transactivate CYP3A4 compared with the parent drugs. Supporting these results, HepG2 cells infected with a recombinant adenovirus expressing human AADAC showed low cytotoxicity and induction potency of CYP3A4 by rifamycins. In addition, CYP3A4 induction in human hepatocytes by rifamycins was increased by transfecting siRNA for human AADAC. Thus, we found that human AADAC was the enzyme responsible for the deacetylation of rifamycins and would affect the induction rate of drug-metabolizing enzymes by rifamycins and their induced hepatotoxicity.
        
Title: In vitro evaluation of inhibitory effects of antidiabetic and antihyperlipidemic drugs on human carboxylesterase activities Fukami T, Takahashi S, Nakagawa N, Maruichi T, Nakajima M, Yokoi T Ref: Drug Metabolism & Disposition: The Biological Fate of Chemicals, 38:2173, 2010 : PubMed
Human carboxylesterase (CES) 1A is responsible for the biotransformation of angiotensin-converting enzyme (ACE) inhibitors such as imidapril and temocapril. Because antidiabetic or antihyperlipidemic drugs are often coadministered with ACE inhibitors in clinical pharmacotherapy, the inhibitory effect of these drugs on CES1A1 enzyme activity was investigated. In addition, the inhibitory effect on CES2 enzyme activity was evaluated to compare it with that on CES1A1. The inhibitory effects were evaluated with 11 antidiabetic and 12 antihyperlipidemic drugs. The imidapril hydrolase activity by recombinant CES1A1 was substantially inhibited by lactone ring-containing statins such as simvastatin and lovastatin and thiazolidinediones such as troglitazone and rosiglitazone. The activity in human liver microsomes was also strongly inhibited by simvastatin and troglitazone (K(i) = 0.8 +/- 0.1 and 5.6 +/- 0.2 muM, respectively). However, statins containing no lactone ring such as pravastatin and fluvastatin did not show strong inhibition. 7-Ethyl-10-[4-(1-piperidono)-1-piperidono]carbonyloxycamptothecin hydrolase activity by recombinant human CES2 was substantially inhibited by fenofibrate (K(i) = 0.04 +/- 0.01 muM) as well as by simvastatin (0.67 +/- 0.09 muM). Other fibrates such as clinofibrate and bezafibrate did not show strong inhibition. Thus, the inhibitory effects of the thiazolidinediones and fenofibrate on CES1A1 and CES2 were different. Some statins such as simvastatin and lovastatin, thiazolidinediones, and fenofibrate might attenuate the drug efficacy of prodrugs biotransformed by CES1A and CES2.
Mammalian carboxylesterase (CES or Ces) genes encode enzymes that participate in xenobiotic, drug, and lipid metabolism in the body and are members of at least five gene families. Tandem duplications have added more genes for some families, particularly for mouse and rat genomes, which has caused confusion in naming rodent Ces genes. This article describes a new nomenclature system for human, mouse, and rat carboxylesterase genes that identifies homolog gene families and allocates a unique name for each gene. The guidelines of human, mouse, and rat gene nomenclature committees were followed and "CES" (human) and "Ces" (mouse and rat) root symbols were used followed by the family number (e.g., human CES1). Where multiple genes were identified for a family or where a clash occurred with an existing gene name, a letter was added (e.g., human CES4A; mouse and rat Ces1a) that reflected gene relatedness among rodent species (e.g., mouse and rat Ces1a). Pseudogenes were named by adding "P" and a number to the human gene name (e.g., human CES1P1) or by using a new letter followed by ps for mouse and rat Ces pseudogenes (e.g., Ces2d-ps). Gene transcript isoforms were named by adding the GenBank accession ID to the gene symbol (e.g., human CES1_AB119995 or mouse Ces1e_BC019208). This nomenclature improves our understanding of human, mouse, and rat CES/Ces gene families and facilitates research into the structure, function, and evolution of these gene families. It also serves as a model for naming CES genes from other mammalian species.
        
Title: Transcriptional regulation of human carboxylesterase 1A1 by nuclear factor-erythroid 2 related factor 2 (Nrf2) Maruichi T, Fukami T, Nakajima M, Yokoi T Ref: Biochemical Pharmacology, 79:288, 2010 : PubMed
Human carboxylesterase (CES) 1A, which is predominantly expressed in liver and lung, plays an important role in the hydrolysis of endogenous compounds and xenobiotics. CES1A is reported to be induced in human hepatocytes by butylated hydroxyanisole, ticlopidine and diclofenac, and the induction is assumed to be caused by oxidative stress. However, the molecular mechanism remains to be determined. In this study, we sought to investigate whether CES1A is regulated by nuclear factor-erythroid 2 related factor 2 (Nrf2), which is a transcriptional factor activated by oxidative stress, and clarify the molecular mechanism. Real-time reverse transcription-PCR assays revealed that CES1A1 mRNA was significantly induced by tert-butylhydroquinone (tBHQ) and sulforaphane (SFN), which are representative activators of Nrf2 in HepG2, Caco-2 and HeLa cells. The induction was completely suppressed with small interfering RNA for Nrf2. In HepG2 cells, the CES1A protein level and imidapril hydrolase activity, which is specifically catalyzed by CES1A, were also significantly induced by tBHQ and SFN. Luciferase assays revealed that the antioxidant response element (ARE) at -2025 in the CES1A1 gene was responsible for the transactivation by Nrf2. In addition, electrophoretic mobility shift assays and chromatin immunoprecipitation assays revealed that Nrf2 binds to the ARE in the CES1A1 gene. These findings clearly demonstrated that human CES1A1 is induced by Nrf2. This is the first study to demonstrate the molecular mechanism of the inducible regulation of human CES1A1.
        
Title: Arylacetamide deacetylase is a determinant enzyme for the difference in hydrolase activities of phenacetin and acetaminophen Watanabe A, Fukami T, Takahashi S, Kobayashi Y, Nakagawa N, Nakajima M, Yokoi T Ref: Drug Metabolism & Disposition: The Biological Fate of Chemicals, 38:1532, 2010 : PubMed
Phenacetin was withdrawn from the market because it caused renal failure in some patients. Many reports indicated that the nephrotoxicity of phenacetin is associated with the hydrolyzed metabolite, p-phenetidine. Acetaminophen (APAP), the major metabolite of phenacetin, is also hydrolyzed to p-aminophenol, which is a nephrotoxicant. However, APAP is safely prescribed if used in normal therapeutic doses. This background prompted us to investigate the difference between phenacetin and APAP hydrolase activities in human liver. In this study, we found that phenacetin is efficiently hydrolyzed in human liver microsomes (HLM) [CL(int) 1.08 +/- 0.02 microl/(min . mg)], whereas APAP is hardly hydrolyzed [0.02 +/- 0.00 microl/(min . mg)]. To identify the esterase involved in their hydrolysis, the activities were measured using recombinant human carboxylesterase (CES) 1A1, CES2, and arylacetamide deacetylase (AADAC). Among these, AADAC showed a K(m) value (1.82 +/- 0.02 mM) similar to that of HLM (3.30 +/- 0.16 mM) and the highest activity [V(max) 6.03 +/- 0.14 nmol/(min . mg)]. In contrast, APAP was poorly hydrolyzed by the three esterases. The large contribution of AADAC to phenacetin hydrolysis was demonstrated by the prediction with a relative activity factor. In addition, the phenacetin hydrolase activity by AADAC was activated by flutamide (5-fold) as well as that in HLM (4-fold), and the activity in HLM was potently inhibited by eserine, a strong inhibitor of AADAC. In conclusion, we found that AADAC is the principal enzyme responsible for the phenacetin hydrolysis, and the difference of hydrolase activity between phenacetin and APAP is largely due to the substrate specificity of AADAC.
        
Title: Different inhibitory effects in rat and human carboxylesterases Takahashi S, Katoh M, Saitoh T, Nakajima M, Yokoi T Ref: Drug Metabolism & Disposition: The Biological Fate of Chemicals, 37:956, 2009 : PubMed
In vitro inhibition studies on drug-metabolizing enzyme activity are useful for understanding drug-drug interactions and for drug development. However, the profile of the inhibitory effects of carboxylesterase (CES) activity has not been fully investigated concerning species and tissue differences. In the present study, we measured the inhibitory effects of 15 drugs and 1 compound on CES activity using liver and jejunum microsomes and cytosol in human and rat. In addition, the inhibition constant (K(i) values) and patterns were determined for the compounds exhibiting strong inhibition. Hydrolysis of imidapril and irinotecan hydrochloride (CPT-11) is catalyzed mainly by CES1 and CES2, respectively. In the inhibition study, imidaprilat formation from imidapril in human liver was strongly inhibited by nordihydroguaiaretic acid (NDGA) and procainamide. The inhibition profile and pattern were similar in human liver and rat liver. The compounds showing potent inhibition were similar between liver and jejunum. The K(i) value of NDGA (K(i) = 13.3 +/- 1.5 microM) in human liver microsomes was 30-fold higher than that in rat liver microsomes (K(i) = 0.4 +/- 0.0 microM). On the other hand, 7-ethyl-10-hydroxycamptothecin (SN-38) formation from CPT-11 was not inhibited except by carvedilol, manidipine, and physostigmine. The K(i) value of physostigmine (K(i) = 0.3 +/- 0.0 microM) in human jejunum cytosol was 10-fold lower than that in rat jejunum cytosol (K(i) = 3.1 +/- 0.4 microM) and was similar to that for manidipine. The present study clarified the species differences in CES inhibition. These results are useful for the development of prodrugs.
        
Title: Human arylacetamide deacetylase is a principal enzyme in flutamide hydrolysis Watanabe A, Fukami T, Nakajima M, Takamiya M, Aoki Y, Yokoi T Ref: Drug Metabolism & Disposition: The Biological Fate of Chemicals, 37:1513, 2009 : PubMed
Flutamide, an antiandrogen drug, is widely used for the treatment of prostate cancer. The initial metabolic pathways of flutamide are hydroxylation and hydrolysis. It was recently reported that the hydrolyzed product, 4-nitro-3-(trifluoromethyl)phenylamine (FLU-1), is further metabolized to N-hydroxy FLU-1, an assumed hepatotoxicant. However, the esterase responsible for the flutamide hydrolysis has not been characterized. In the present study, we found that human arylacetamide deacetylase (AADAC) efficiently hydrolyzed flutamide using recombinant AADAC expressed in COS7 cells. In contrast, carboxylesterase1 (CES1) and CES2, which are responsible for the hydrolysis of many drugs, could not hydrolyze flutamide. AADAC is specifically expressed in the endoplasmic reticulum. Flutamide hydrolase activity was highly detected in human liver microsomes (K(m), 794 +/- 83 microM; V(max), 1.1 +/- 0.0 nmol/min/mg protein), whereas the activity was extremely low in human liver cytosol. The flutamide hydrolase activity in human liver microsomes was strongly inhibited by bis-(p-nitrophenyl)phosphate [corrected], diisopropylphosphorofluoride, and physostigmine sulfate (eserine) but moderately inhibited by sodium fluoride, phenylmethylsulfonyl fluoride, and disulfiram. The same inhibition pattern was obtained with the recombinant AADAC. Moreover, human liver and jejunum microsomes showing AADAC expression could hydrolyze flutamide, but human pulmonary and renal microsomes, which do not express AADAC, showed slight activity. In human liver microsomal samples (n = 50), the flutamide hydrolase activities were significantly correlated with the expression levels of AADAC protein (r = 0.66, p < 0.001). In conclusion, these results clearly showed that flutamide is exclusively hydrolyzed by AADAC. AADAC would be an important enzyme responsible for flutamide-induced hepatotoxicity.
OBJECTIVE: Human carboxylesterase (CES) 1A1 gene (14 exons) and CES1A3 pseudogene (six exons) are inverted and duplicated genes in a reference sequence (NT_010498). In contrast, earlier studies reported the CES1A2 gene (14 exons) instead of the CES1A3 pseudogene. The sequences of the CES1A2 gene downstream and upstream of intron 1 are identical with those of the CES1A1 and CES1A3 genes, respectively. A CES1A1 variant of which exon 1 is converted with that of the CES1A3 gene (the transcript is CES1A2) has recently been identified. We sought to clarify the confusing gene structure of human CES1A. METHODS: A panel of 55 human liver as well as 318 blood samples (104 Caucasians, 107 African-Americans, and 107 Japanese) was used to clarify the gene structures of CES1A1, CES1A2, and CES1A3. Real-time reverse transcription-PCR and western blot analysis were carried out. Imidapril hydrolase activity in human liver microsomes and cytosol was determined by liquid chromatography-mass spectrometry (LC-MS)/MS. RESULTS: By PCR analyses, we found that the CES1A2 gene is a variant of the CES1A3 gene. Four haplotypes, A (CES1A1 wild type and CES1A3), B (CES1A1 wild type and CES1A2), C (CES1A1 variant and CES1A3), and D (CES1A1 variant and CES1A2), were demonstrated. Ethnic differences were observed in allele frequencies of CES1A1 variant (17.3% in Caucasians and African-Americans and 25.2% in Japanese) and CES1A2 gene (14.4% in Caucasians, 5.1% in African-Americans, and 31.3% in Japanese). In human livers whose diplotype was A/A and C/C or C/D, no CES1A2 and CES1A1 mRNA was detected, respectively. In the other participants, the CES1A1 mRNA levels were higher than the CES1A2 mRNA levels. The CES1A proteins translated from CES1A1 mRNA and CES1A2 mRNA were detected in both human liver microsomes and cytosol fractions suggesting that the differences in exon 1 encoding a signal peptide did not affect the subcellular localization. Imidapril hydrolase activities reflected the CES1A protein levels. CONCLUSION: We found that the CES1A2 gene is a variant of the CES1A3 pseudogene. The findings presented here significantly increase our understanding about the gene structure and expression properties of human CES1A.
        
Title: Regulation of insulin-like growth factor binding protein-1 and lipoprotein lipase by the aryl hydrocarbon receptor Minami K, Nakajima M, Fujiki Y, Katoh M, Gonzalez FJ, Yokoi T Ref: Journal of Toxicological Sciences, 33:405, 2008 : PubMed
The aryl hydrocarbon receptor (Ahr), a ligand-activated transcriptional factor, mediates the transcriptional activation of a battery of genes encoding drug metabolism enzymes. In the present study, we investigated the hepatic mRNA expression profile in Ahr-null (Ahr KO) mice compared to wild-type mice by microarray analysis to find new Ahr target genes. Pooled total RNA samples of liver extracted from 7- and 60-week-old Ahr KO or wild-type mice were studied by DNA microarray representing 19,867 genes. It was demonstrated that 23 genes were up-regulated and 20 genes were down-regulated over 2 fold in Ahr KO mice compared with wild-type mice commonly within the different age groups. We focused on insulin-like growth factor binding protein-1 (Igfbp-1) and lipoprotein lipase (Lpl) that were up-regulated in Ahr KO mice. The higher expression in Ahr KO mice compared to wild-type mice were confirmed by real-time RT-PCR analysis. In the wild-type mice but not in the Ahr KO mice, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) treatment increased the Igfbp-1 and Lpl mRNA levels. The expression profile of Igfbp-1 protein was consistent with that of Igfbp-1 mRNA. Since Lpl is the primary enzyme responsible for hydrolysis of lipids in lipoproteins, the serum triglyceride levels were determined. Indeed, the serum triglyceride levels in Ahr KO mice was lower than that in wild-type mice in accordance with the Lpl mRNA levels. Contrary to our expectation, TCDD treatment significantly increased the serum triglyceride levels in wild-type, but did not in Ahr KO mice. These results suggest that serum triglyceride levels are not correlated with hepatic Lpl expression levels. In the present study, we found that Ahr paradoxically regulates Igfbp-1 and Lpl expressions in the liver.
        
Title: Allosteric kinetics of human carboxylesterase 1: species differences and interindividual variability Takahashi S, Katoh M, Saitoh T, Nakajima M, Yokoi T Ref: J Pharm Sci, 97:5434, 2008 : PubMed
Esterified drugs such as imidapril, derapril, and oxybutynin hydrolyzed by carboxylesterase 1 (CES1) are extensively used in clinical practice. The kinetics using the CES1 substrates have not fully clarified, especially concerning species and tissue differences. In the present study, we performed the kinetic analyses in humans and rats in order to clarify these differences. The imidaprilat formation from imidapril exhibited sigmoidal kinetics in human liver microsomes (HLM) and cytosol (HLC) but Michaelis-Menten kinetics in rat liver microsomes and cytosol. The 2-cyclohexyl-2-phenylglycolic acid (CPGA) formation from oxybutynin were not detected in enzyme sources from rats, although HLM showed high activity. The kinetics were clarified to be different among species, tissues, and preparations. In individual HLM and HLC, there was large interindividual variability in imidaprilat (31- and 24-fold) and CPGA formations (15- and 9-fold). Imidaprilat formations exhibited Michaelis-Menten kinetics in HLM and HLC with high activity but sigmoidal kinetics in those with low activity. CPGA formations showed sigmoidal kinetics in high activity HLM but Michaelis-Menten kinetics in HLM with low activity. We revealed that the kinetics were different between individuals. These results could be useful for understanding interindividual variability and for the development of oral prodrugs.
As a base for human transcriptome and functional genomics, we created the "full-length long Japan" (FLJ) collection of sequenced human cDNAs. We determined the entire sequence of 21,243 selected clones and found that 14,490 cDNAs (10,897 clusters) were unique to the FLJ collection. About half of them (5,416) seemed to be protein-coding. Of those, 1,999 clusters had not been predicted by computational methods. The distribution of GC content of nonpredicted cDNAs had a peak at approximately 58% compared with a peak at approximately 42%for predicted cDNAs. Thus, there seems to be a slight bias against GC-rich transcripts in current gene prediction procedures. The rest of the cDNAs unique to the FLJ collection (5,481) contained no obvious open reading frames (ORFs) and thus are candidate noncoding RNAs. About one-fourth of them (1,378) showed a clear pattern of splicing. The distribution of GC content of noncoding cDNAs was narrow and had a peak at approximately 42%, relatively low compared with that of protein-coding cDNAs.
Expression of drug-metabolizing enzymes including cytochrome P450 (CYP) and flavin-containing monooxygenase (FMO) in various tissues of Suncus murinus (Suncus) were examined. Northern blot analysis showed that mRNAs hybridizable with cDNAs for rat CYP1A2, human CYP2A6, rat CYP2B1, human CYP2C8, human CYP2D6, rat CYP2E1, human CYP3A4 and rat CYP4A1 were expressed in various tissues from Suncus. The mRNA level of CYP2A in the Suncus lung was very high. Furthermore, it was found that the level of CYP2A mRNA in the Suncus lung was higher compared to the Suncus liver. The expression level of mRNA hybridizable with cDNA for human CYP3A4 was very low. The presence of CYP3A gene in Suncus was proven by the induction of the CYP with dexamethasone. Very low expression levels of mRNAs hybridizable with cDNAs for rat FMO1, rat FMO2, rat FMO3 and rat FMO5 were also seen in Suncus liver. No apparent hybridization band appeared when human FMO4 cDNA was used as a probe. The hepatic expression of mRNAs hybridizable with cDNAs for UDP-glucuronosyltransferase 1*6, aryl sulfotransferase, glutathione S-transferase 1, carboxyesterase and microsomal epoxide hydrolase in the Suncus were observed. These results indicate that the Suncus is a unique animal species in that mRNAs for CYP3A and FMO are expressed at very low levels.